1. Technical Field
The invention is related to solar power, and more particularly, to modules for converting incident optical radiation to microwave radiation and transmitting the microwave radiation.
2. Related Technology
Space solar power systems have been contemplated since the 1960s, for collecting the sun's solar energy and transmitting it to earth. Early concepts involved large sun-tracking photovoltaic arrays feeding power to a separate microwave conversion and transmitting module. As contemplated, these systems required power cabling for the low voltage current from the photovoltaic array and a gimbaled connection between the photovoltaic array and the microwave module.
A NASA/DOE space solar power concept circa 1980 proposed using a photovoltaic (PV) array of multi-kilometer dimension to supply electrical power to an antenna system that would convert the power to microwaves and beam it to earth. The PV array was proposed to track the sun while the antenna would track the receiver on earth. This design, while promising, had several difficulties. First, a large mass of copper wiring would be needed to carry low voltage current and transfer the current through slip rings. Second, a large supporting structure would be required for the flat PV array. Third, time consuming handwork by a number of astronauts would be needed to complete the on-orbit assembly.
Another concept known as the “Integrated Symmetrical Concentrator” proposed using a two-axis reflector array that tracks the sun continuously to direct sunlight in a nadir direction to a single compact module, called a sandwich cell array. This system allows two-axis sun tracking while the microwave antennas remain pointing toward the earth. The sandwich cell array combines a photovoltaic array, electric to microwave conversion, and nadir-directed microwave transmission. PV and microwave systems are back-to-back in the “sandwich” power conversion module, eliminating long power cables and slip rings. Solar concentration reduces the number of PV cells. However, waste heat from PV and microwave devices creates high temperatures that significantly reduce system efficiency. Further, the problems of structural mass to maintain the flat disc module, and on-orbit assembly of module, remain.